Usefull Mac Applications

Hey Everyone. I hope you guys are doing well.
If you dont wanna read just check out the video below.

http://www.youtube.com/watch?v=OVu90ecNNlA

Basically, I just want to ask which applications you guys use on our Mac Machines. I did see the thread "Links to Software Recommendation Threads". But a lot of the threads there are quite old. Plus its a lot of reading.
If some of you could just list 2-3 Apps you guys use which you think are important or useful I would really appreciate it.
I am sorta looking more towards productivity apps, but if you've got some other ones, let me know.
Thanks.

Thanks! That was very helpful!
I just started using Better Touch Tool and love it!!
I just have a question regarding that tool. Is it possible to open an application like "safari" or "ical" using a gesture? I tried searching a way but couldn't really get any help. I have seen people using gestures to open applications. Is this possible? and if so which application does it?

Thanks.